Belt tensioners are known that have a drive unit and a power transmission element, which engages on a drive element when the drive unit is activated. Several balls arranged in a row serve for example as the power transmission element, these balls being initially stored in a tube and being acted upon by a high pressure when a gas generator, which constitutes the drive unit, is activated. The balls are thereby pushed forward out of the tube and drive the drive element, which is coupled to the belt spool.
The invention provides a belt tensioner which is distinguished by a particularly simple method of manufacture, a low weight and a variable and therefore space-saving housing in the vehicle.